Here is how I think Wotc should handle this.
What sets are eligible: I think that they should pull primarily from pre-modern sets. But not limit themselves. the draft experience should be king. I think their aim should be "powered cube" whereas Modern Masters was "cube".
What frames: Obviously they are going to use modern frames for P9 based on the pictures. I think they will hold the old art/frames for a promo (which I believe should be incredibly limited). But the set itself should be old frames. all the "not yet released" cards like virtues ruin need to look like Eternal cards. What I think would be really cool is putting some cards into old frames that have only been released in new frames. I'm think cards that already see eternal play like noble heirarch.
Lands?: no duals. in fact I don't think they should include anything from MED4. I think they should have MED4 events leading up to the release (including this winter). that way they get some of the new converts $ starting now.
Mythics: I think the mythics should be good cards. I think they should include at least 2 planeswalkers (in old frames) and some others that are good in vintage like Griselbrand.
Eternal reprints: I think they need to reprint some stuff from saga/masques/etc. I don't think they should reprint anything that is restricted (cept LED for legacy) and nothing with the old art. Wasteland absolutely needs to be reprinted... I think they need to make it rare though.
FoW: there needs to be a playset of Fow for every pset of P9. at a minimum. Wotc should know what number this is and if FoW needs to be reprinted to get this. I bet they do. it has to be mythic if they do. and I think it should have a third art. With Jace.
Limited format: yeah powered cube should be the feel they go for. I'm thinking Storm, reanimator/show/oath/sneak attack and some sick tribal, slivers (muscle, sinew, predatory etc) full merfolk (including 7e art in BB), elves, goblins, vial.
The release: we need to have at least monthly old set drafts starting now. MED, saga, masques, Mirage, Tempest. build the hype. I think they should NOT have VM phantom events. we need the cards.
going forward: they need to create more incentive to play Vintage. card availability is one thing, value is another. people won't buy in if they can't get real prizes. having a $2000 deck to win 11 packs is lame. I think they ned a vintage only MOCS. with top prize being original art Power.. with foil being only for mocs champ (yeah like 1 playset of original art P9 per year level rarity)